Tube formation is an important process in the development of many organs, including the lung, kidney, intestine, and heart, so it is critical to understand this process at both the cellular and molecular level. The goal of this proposal is to elucidate the role of multiple inositol polyphosphate phosphatase (Mipp1) in Drosophila trachea development, which is one of the best model systems for studying tubular organogenesis. Mipps are the main enzymes to dissipate the high order inositol polyphosphates (InsP), which are important second messengers for many important cellular processes. The biological function of Mipps is very poorly understood. mipp1 was identified as a downstream target of Trachealess (Trh), a critical transcription regulating the entire process of trachea formation. A knockout of mipp1 was successfully generated and its phenotypic characterization revealed significant dorsal trunk elongation and ganglionic branch mismigration defects. These preliminary results lead to the hypothesis that Mipp1 regulates the production of molecules involved in limiting dorsal trunk length and directing ganglionic branch migration. Part A of specific aim 1 will define the role of Mipp1 in tracheal development by analyzing the tracheal phenotypes associated with the loss and overexpression of Mipp1. Part B of specific aim 1 will reveal whether Mipp1 functions through the known pathways that affect tracheal dorsal trunk tube size control and ganglionic branch migration or through a novel pathway(s). Specific aim 2 will test if Drosophila Mipp2 compensates for Mipp1 activity by comparing the tracheal phenotypes of mipp1 knockout and mipp1 mipp2 double null mutants. Specific aim 3 will reveal whether Mipp1 functions through the generation of InsP4, InsP3 from InsP5 and InsP6 or through the generation of 2- phosphogylcerate from 2, 3-biphosphoglycerate to regulate tube size control and branch migration. The genes encoding enzymes in parallel pathways will be manipulated to build up Mipp1 substrates or products to learn which molecules are relevant to the tracheal defects observed in mipp1mutants. The analysis of Mipp function in the very tractable system of the Drosophila embryonic trachea is likely to provide insight into how this highly conserved family of proteins functions in higher animals.